This invention relates to a variable resistance device, and in particular to such a device having means to restrain rotation of the shaft thereof except upon application of a relatively large magnitude rotational force.
Variable resistance devices, such as potentiometers, are employed in many varied applications. In many applications, the resistance device is positioned adjacent operating machinery whereat the device is exposed to vibrational forces.
Additionally, in numerous applications, many resistance devices are often installed adjacent each other in an operating panel or console. In such applications, there is constant movement of personnel about the panel or console. In the course of such personnel movement, inadvertent and undesirable readjustment of the setting of the device may occur as a result of unintentional contact between personnel and device. Additionally, many times a person or operator, in attempting to set a resistance device to a desired resistance value, may accidentally disturb the setting of an adjacent resistance device.
To prevent accidental changes in the resistance value of a variable resistance device, many of such devices employ means to prevent rotation of the device except upon application of a predetermined rotational force to the shaft thereof. Many of such rotation preventing means include means to provide an axial load on the shaft or other rotary components of the variable resistance device to prevent the undesired rotation. Although, such axial load producing means effectively prevent undesired rotation, the axial loading tends, in some instances, to push the various components of the resistance device apart. Accordingly, it has been found that it is more desirable to provide radially acting forces to prevent undesired setting changes.
Heretofore, the known means for producing radial restraining forces have been installed and become operational prior to the total assembly, calibration, and inspection of the resistance device.
During calibration and inspection procedures, the rotary assembly of the resistance device is rotated many times to insure a high degree of accuracy. The additional force required during calibration and inspection to overcome the frictional force created to prevent undesired rotation decreases production and has a tendency to increase worker fatigue.